Development of self-crimping yarns for generating high bulk has been one of the active areas for producing differentiated products. The self-crimping yarns can be used directly in stretch fabrics where the high crimp level of the yarns allows higher stretch in the fabrics. The filaments thus produced would have longer lasting crimp as it is developed in-situ since the two polymeric components are integrally bonded in each individual filament.
Various approaches have been explored to get the self-crimping characteristics. These include different cross-sections and various bicomponent geometries, namely, side-by-side, eccentric sheath-core etc. By and large, putting the two polymeric components in a side-by-side combination is the most widely used method to produce high bulk filaments.
A prior art survey indicates use of different polyamides in pairs or also polyethylene terephthalate (PET) with chemically different polyesters, such as, polybutylene terephthalate (PBT) or cross-linked polyesters. In some studies both the components are chemically modified and then spun into bicomponent yarns thus rendering self-crimping effect on to the yarns. Others have used elastomers as one of the components to get the desired effect. More recently, polymers like poly(trimethylene terephthalate) (PTT) have been used with PET or PBT, etc. for achieving the bulk characteristics.
Another approach is to use differential cooling of filaments in the spin line for producing high bulk filaments using a single polymer. Moreover, most of the methods employed in the prior art involve a two-step process, which comprises LOY spinning followed by drawing/draw-texturing. The present invention is a one step process for producing high bulk fully drawn yarns (FDY) or a two step process for getting textured yarns.
Some researchers have also tried Poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) wherein the Poly(butylene terephthalate) was cross-linked. In one of the inventions in the past, the PET and PBT are spun on bicomponent machine but the process of manufacture involved online cold drawing of the filaments. Polyester essentially requires hot drawing so as to have long term dimensional stability. In another recent process, PET and PBT are spun in bicomponent fashion but again the method employed was a two-stage process.
French patent 1,486,035 discloses a composite polyester made up of poly(ethylene terephthalate) and poly(ethylene terephthalate) cross linked with trimethylol propane.
A side-by-side or eccentric sheath-core bicomponent fiber wherein each component comprises poly(trimethylene terephthalate) differing in intrinsic viscosity (IV) and wherein at least one of the components comprises styrene polymer dispersed throughout the poly(trimethylene terephthalate) by partially oriented yarn (POY) or fully drawn yarn FDY route is disclosed in U.S. Pat. No. 6,641,916.
Polyamide conjugate filaments are prepared by a spinstretch process wherein two polyamides (e.g. two nylon 66 polymers) having different terminal velocity distances are melt spun to form filaments in which the polymers are arranged in an eccentric/side-by-side configuration along the length of the filaments. The filaments are then stretched in-line at a stretch ratio greater than 1.0 prior to their being collected with the processing conditions and polyamides being selected to provide filaments having a high level of high-load crimp and a low level of boiling water shrinkage which is disclosed in U.S. Pat. Nos. 4,601,949 and 4,740,339.
While, the present invention is primarily based on two homopolymers and a reference of faster crystallizing copolymer is given.
U.S. Pat. No. 6,548,429 discloses a polymer yarn comprising a bicomponent yarn and a second yarn combined to form a single yarn. The bicomponent yarn comprises two components, each comprising a fiber-forming polymer and each preferably having different shrinkages, which effectuate a bulking effect. This may be obtained either by using different polymers or using polymers having different relative viscosities.
The conjugate fibres based on PET, PBT and PTT are disclosed in U.S. Pat. No. 6,306,499. This essentially is a process in which spinning is carried out at 1200 mpm and drawn in a separate process. Spinning polyesters at 1200 meters per minute gives a yarn that is termed as a LOY, which will have less orientation and lower shelf life. However, the subject of present invention is either a one step process with PET and PBT or PET with PTT etc. wherein winding is carried out at significantly higher speeds i.e. 3500 to 4500 mpm. Alternatively the process can be a two-stage POY and textured process.
U.S. Pat. No. 6,153,138 and U.S. Pat. No. 4,740,339 patents disclose the use of different Nylon polymer having differential relative viscosity to get the self-crimping effect.
But the present invention is primarily based on polymers having different levels of crystallizability.
A melt-spinning process for producing self-crimping, nylon 66 carpet yarn at spinning speeds of, for example 4000 meters per minute is disclosed in U.S. Pat. No. 4,975,325. The process utilizes polymer having a relative viscosity (RV) of at least 50 and containing a sufficient amount of a chain branching agent.
U.S. Pat. No. 4,661,404 discloses the polyester filaments having a generally oblong, qudrolobal cross section are produced with periodic variations in thickness along the length of yarn and the yarn being capable of developing crimp when thermally treated in a relaxed state and having a crimp-to-shrinkage ratio of at least 0.25.
The combination of elastic component and an inelastic component is disclosed in U.S. Pat. No. 4,554,121 to produce latent self-crimping yarns. While in the present invention elastic component in the stretch fabrics have been replaced by bicomponent polyester filaments, which will have easy care and easy processing characteristics.
U.S. Pat. No. 4,405,686 discloses a stretchable crimped elastic yarn, which is prepared from composite components respectively comprising thermoplastic elastomer and non-elastomeric polyamide or polyester, and each of the individual constituents has a cross section of a compressed flat shape like a cocoon or oval.
Polyolefins and polyester combination has been disclosed in U.S. Pat. No. 4,424,258 for getting self-crimping yarns. The degree of adhesion between polyolefin and polyester is low thus the chances of boundary separation are good. Moreover polyolefins will give rise to dyeing problems. While the present invention basically makes use of two kinds of polyesters and hence the degree of adhesion will be high and dyeing is not an issue.
JP 2004277930 discloses process of producing self-crimping yarns by use of PET and PTT as two polymer components in Bicomponent yarn produced by way of spinneret modification. While the desired product attributes in the present invention is achieved without any spinneret modification.
WO2001053573 discloses making of PTT/PET bicomponent yarns by way of quench modification and drawing at high speeds of the order of 5500 m/min. While the present invention focuses use of standard commonly used hardware for producing the high bulk yarns.
U.S. Pat. No. 6,811,873 discloses the art of producing self-crimping fibres by bicomponent spinning technology. The self-crimping fibres reported here comprise poly(ethylene terephthalate) based fibres of differing molecular weight.
The use of PET and PBT bicomponent yarns are disclosed in U.S. Pat. No. 4,217,321 wherein PET and PBT were extruded in a side-by-side cross section and are cold drawn in an isolated zone. The yarn prepared by this reported process may not be thermally stable. While the present invention intends to provide thermally stable yarn by using a simple process which doesn't involve cold drawing or isolated zone.
A prior art survey indicates use of different polyamides in pairs or also PET with chemically different polyesters, such as, PBT or cross-linked polyesters (U.S. Pat. Nos. 4,186,168, 4,117,194).
As per prior art survey majority of the work is focused on polyamides and their copolymers. The approaches employed include polyamides with different melt viscosity levels, and use of thermoplastic elastomer as one of the components, besides polyamide or polyester (U.S. Pat. Nos. 6,015,618, 6,153,138, 5,972,502, 5,948,528 4,975,325, 4,740,339, 4,405,686, 4,271,233, etc).
In prior art, majority numbers of disclosures indicate use of thermal treatment for getting fully crimped yarns. In the prior art, polymers used to prepare fully crimped yarns are either poly(ethylene terephthalate) with or without chemical modification or along with different combination of polymers.
Thus the processes reported in the prior art to produce the high bulk yarn are a two stage process which is time consuming and uneconomical.
In prior art the focus was on modification of the standard bicomponent spinning hardware such as quench modification or draw zone modification which incurs additional capital cost.
The polymer combination used in the prior art for preparing high bulk yarns, polyester and polypropylene or polyester and nylon, have very little adhesion power and tend to split during spinning/drawing process or during subsequent cloth washings. Thus the stretch attributes may not be durable.
The polymer combination used in the prior art to prepare high bulk yarn comprises polypropylene, which may have dyeing problems.
The stretch attributes are required in fabrics for various end uses such as sportswear, suitings, swimwear, ladies blouses, shirtings etc. The stretch gets developed after heat treatment like boiling water shrinkage or it is latent in the yarn. The end use segments are divided into ‘comfort stretch’ wear and ‘power stretch wear’ fabrics. But the scope of manufacturing fabrics with desired stretch attributes is limited due to the cumbersome manufacturing process. There is need to develop a simple and industrially viable process to manufacture the self-crimping high bulk yarn which have durable stretch attributes.
The present invention discloses use of two viscoelastic fiber forming polymer components with different rates of crystallization, or differential orientation or combination thereof which leads to differential morphological characteristics when spun and drawn online in a side-by-side bicomponent geometry causing stretch attributes. By varying process conditions in spinning/drawing process one can generate controlled differential in crystallinity or orientation to achieve desired yarn characteristics so that the required attributes like stretch and bulk can be developed in the fabric form. The self-crimping high bulk yarns of the present invention have stretch attributes which are durable.